1. Field of the Invention
The present invention relates to an improved seal for fluid tight joints and a method of making the same and may be of the type generally classified in the U.S. Patent Office with joint packing, wedging portions, Class 277, Sub-class 190. The improved apparatus or seal is particularly useful for providing a corrosion resistant, fluid tight joint between tubular members having different coefficients of thermal expansion and which are exposed to ambient temperature changes in a corrosive environment.
2. Description of the Prior Art
O-ring seals made of tetrafluorethylene have been employed to provide corrosion resistant fluid tight joints between members having different coefficients of thermal expansion. Such seals however have not provided entirely satisfactory fluid tight sealing joints because of their inherently stiff and smooth peripheral surfaces. O-rings which are made of more deformable materials such as natural rubber or synthetic rubber, and which provide better sealing surfaces have been unsatisfactory because of their inability to resist the corrosive effects of the environment. Corrosion resistant epoxy bonding materials have also been employed but are unsatisfactory because of their inability to withstand, without cracking and leaking, the ambient temperature changes to which the fluid tight joint is exposed. More recently a seal has been made which overcomes some of the aforementioned deficiencies by first wrapping several layers of a deformable plastic tape on a mandrel, mounting a pair of sliding dies on the mandrel on opposite sides of the tape, moving the dies toward one another to effect the compression of ends of the tape into a laminated sealing ring member and then assembling the compressed seal as a sealing ring between two annular members. This type of fluid tight seal and method of making same is disclosed in the above referenced Arthur E. Gealt U.S. Pat. No. 3,854,731.
The aforementioned construction is an improvement over the prior art methods that have previously been employed to make fluid tight seals. However, the numerous steps of manufacturing required e.g., to wrap layers of plastic tape upon a mandrel, to compress the ends of the tape on the mandrel into an annular sealing ring, to remove the ring from the mandrel and mount it as a sealing ring between two annular members has been found to be too costly. When such a seal is retained by a clamping ring and a glass tube of a prescribed size, such a seal will satisfactorily seal a joint formed between the clamping ring and the glass tube. However, when such an annular sealing ring is mounted between two annular plastic members and the space between these members into which the sealing ring is applied is greater than the normal amount of space for which the sealing ring was designed, as occurs with normal tolerances, there is a potential for the joint formed by that sealing ring to leak. Such leakage occurs because those plastic members have a tendency to creep, especially when they are subjected to temperature cycles.